Hydraulic power supply system

ABSTRACT

An hydraulic power supply system including a pump, an accumulator and a variable flow rate valve connected to by-pass to the reservoir that portion of the pump output which exceeds current system demand. This is accomplished by varying the flow rate of the by-pass valve in accordance with the quantity of fluid stored in the accumulator.

Waited States Patent ['91 ayner et al.

1March 13, 1973 HYDRAULIC POWER SUPPLY SYSTEM [75] Inventors: Paul F.Hayner, Lexington, Mass;

David G. Eldridge, Nashua, NH.

Sanders Associates, Inc., Nashua, NH,

Filed: July 23, 1971 Appl. No.: 165,554

[73] Assignee:

US. Cl ..4l7/304, 417/307 Int. Cl ..F04b 49/00 Field of Search..4l7/304, 307, 308, 310, 299

[5 6] References Cited UNITED STATES PATENTS 2,313,351 Magnuson..4l7/307 2,852,033 9/1958 Orser ..4l7/307 Primary Examiner-Carlton R.Croyle Assistant Examiner-Richard Sher Attorney-L0uis Etlinger ABSTRACT2 Claims, 2 Drawing Figures ls- LOADS F2: 2 5' 23 l \S 27 \Q.

: L k- 2 I I l8 l7 l3 7 LOADS INVENTORS PAUL F. HAYNE'F? DAVID G.ELDRIDGE BY f pf glqm ATTORNEY PATENTEBHARmma 3 0,

sum 2 or 2 X il 2 5e '2 LINE INVENTORS PAUL F. HAYNER #12 DAVID G.ELDRIDGE FIG. .2 BY [16% ATTORNEY HYDRAULIC POWER SUPPLY SYSTEM FIELD OFTHE INVENTION This invention relates generally to hydraulic power supplysystems and particularly to such systems which automatically make asupply of fluid under pressure available for actuating useful loaddevices.

BACKGROUND OF THE INVENTION A typical system of the prior art includes acontinuously running pump which delivers fluid from a reservoir througha check valve to an accumulator and to a load line. A by-pass valve isconnected between the high pressure side of the pump and the reservoir.At the start of operations, the by-pass valve is closed and the pumpsupplies the load and charges the accumulator. When the accumulatorbecomes fully charged, the bypass valve is automatically opened,diverting the entire flow of the pump to the reservoir while the load issupplied from the accumulator, When the accumulator becomes nearlydepleted, the by-pass valve is automatically closed, whereupon the pumpagain delivers fluid to both the load and the accumulator.

Systems as described above, although widely used, are subject to certaindisadvantages. For example, the accumulator is continually being cycledfrom empty to full, causing rapid wear of the tail rod seals. As anotherexample, the wide and frequent fluctuations in pressure cause rapiddeterioration and frequent failure of hoses, pipes; seals and pumps.

It is a general object of the present invention to provide an improvedhydraulic power supply system.

Another object is to provide such a system in which the fluctuations inline pressure are minimized.

Another object is to provide such a system in which the cycling of theaccumulator is minimized.

SUMMARY OF THE INVENTION Briefly stated, in a system incorporating thepresent invention, the by-pass valve is one in which the flow rate iscontinuously variable in response to the quantity of fluid stored in theaccumulator .so as to divert continuously to the reservoir substantiallythat portion of the output of the pump which exceeds the current systemdemand.

BRIEF DESCRIPTION OF THE DRAWING For a clearer understanding of theinvention, reference may be made to the following detailed descriptionand the accompanying drawing, in which:

FIG. 1 is a schematic diagram illustrating the principles of theinvention; and

FIG. 2 is a schematic diagram of a preferred embodiment of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENT nected to a source 16 of a gas, suchas nitrogen, under pressure. A by-pass valve 17 has its inlet 18connected to the line 13 and its outlet 19 connected to the reservoir12. It is shown schematically and includes a portion 21 which, inresponse to an increase in applied fluid pressure and working against aspring 22, increases the flow of fluid from inlet 18 to outlet 19.

A variable pressure divider, denoted generally by the referencecharacter 23, comprises a flxed restrictor 24 and a variable restrictor25 serially connected between the line 13 and the reservoir 12.Preferably a filter 26 is inserted between the line 13 and therestrictors. Each restrictor provides a certain amount of resistance tothe flow of fluid so that the pressure at their junction depends uponthe pressure in the line 13 and the relative values of the tworestrictors. The restrictor 25 is mechanically connected to have itsmagnitude varied continuously in accordance with the position of thepiston 15 which in turn is indicative of the quantity of fluid currentlystored in the accumulator 14. In the present example the mechanicalconnections are such that the magnitude of the restrictor 25 increasesas the amount of fluid stored in the accumulator increases. The junction27 is connected to the pressure responsive portion 21 of the valve 17.

The pump 11 is preferably (but not necessarily) a constant displacementpump which delivers fluid at a constant rate of flow determined by itscapacity into the line 13. A portion of this rate of flow, determined bythe system demand, is bypassed to the reservoir 12 by the valve 17. Thesystem demand is the sum of the small flow through the pressure divider,the flow through the load and the flow to the accumulator. The latter,of course, may be positive or negative in sign.

In operation, the pump 11 furnishes the fluid required by the pressuredivider, the loads, and the accumulator. A portion of the pump output isdiverted to the reservoir 12 by the valve 17. If the load shouldincrease, it would tend to draw fluid from the accumulator l4, reducingthe quantity of fluid stored therein. Such reduction would decrease themagnitude of the restrictor 25 thus decreasing the pressure dropthereacross and decreasing the pressure at the junction 27. Suchdecrease would allow the spring 22 to decrease the rate of flow of fluidthrough the valve 17, thus making a greater rate of flow available tothe load and to the accumulator. The system would soon stabilize withthe valve 17 diverting to the reservoir 12 that portion of the output ofthe pump 11 which exceeds the then current system demand. If the loadshould then decrease, a similar but opposite sequence of events wouldoccur. Flow of fluid into the accumulator would tend to increase, thusincreasing the quantity of fluid stored therein, increasing themagnitude of the restrictor 25, increasing the pressure at the junction27 and increasing the rate of flow through the valve 17 until the systemagain stabilized with the flow through the valve 17 again substantiallyequal to the excess of pump output over the new system demand.

Referring now to FIG. 2, a preferred embodiment of the invention shownschematically in more detail. Components identical or comparable tothose of FIG. 1 are denoted by the same reference characters. The pump11 draws fluid from the reservoir 12 and delivers it through a checkvalve 31 to the line 13 which, as before, is connected to the load andto the accumulator 14. The piston is connected to a tail rod 32 whichextends through a seal 33 to the exterior of the accumulator 14. Thetail rod 32 actuates a limit switch 36 through any suitable mechanicallinkage, shown schematically by the dotted line 37. In the position ofthe parts shown, the accumulator 14 is full and the movable arm 38 ofthe switch engages a fixed contact 41. When the accumulator is nearlyempty, the arm 38 engages a fixed contact 42. The moveable arm 38 isconnected to a terminal 43 which in turn is connected to a conductor X.The contacts 41 and 42 are connected to conductors Y and Z respectively.

The tail rod 32 carries a short arm 44 the end of which is connected toan endless flexible member 45 such as a light chain which drives twosprockets 46 and 47. The sprocket 47 is fastened to a hub 48 to which isalso fastened a gear 49 which engages a sector of a gear 51 fastened toa hub 52, to which is also fastened a cam 53. The latter is engaged by aroller 54 pivoted on one end of an arm 55 the other end of which ispivoted at point 56.

Fluid from the line 13 flows through the filter 26 and the conduit 58 tothe restrictor 24 which comprises several orifices in series. Fluid thenflows through a nozzle 61 and impinges on the closely adjacent flatsurface of one end of a member 62 fastened to a resilient spider 63which holds the member 62 in place radially. The nozzle 61 and themember 62 are comparable to the restrictor 25 of FIG. 1 and are denotedtogether by this reference character in FIG. 2. The other end of themember 62 bears against a spring seat 65 against which a spring 66 bearswhich urges the member 62 towards the nozzle 61 in opposition to fluidpressure. The other end of the spring 66 bears against another springseat 67 which in turn bears against one end of a rod 68 the other end ofwhich engages an intermediate portion of the arm 55.

The valve 17 includes a body formed with a generally cylindrical boreincluding end spaces 71 and 72 and ports 73, 74, 75 and 76. Within thebore is a spool 77 formed with three lands 78, 79 and 81. The end space72, to the left as viewed in FIG. 2, is connected by a conduit 82 to thereservoir 12 and contains a spring 83 bearing against spring seats 84and 85, the former bearing against the body of the valve 17 and thelatter bearing against the land 81, urging the spool 77 to the right.The end space 71 is connected by a conduit 86 to the control fluidpressure as will be more fully explained. The ports 74 and 76 maycontain a plurality of restrictors 87 and 88, respectively, which may bemany small diameter tubes or pipes but which preferably comprise aseries of plates formed with baffles on one or both faces as more fullydescribed in the copending application of Paul F. I-Iayner and RichardJ. Brockway, Ser. No. 093,]92 filed Nov. 27, 1970 for Fluid FlowRestrictor, now US. Pat. No. 3,688,800 issued Sept. 5, 1972, andassigned to the same assignee as is the instant application. The port 73is connected by a conduit 89 to the high pressure side of the pump 11.Fluid flows from the conduit 89 through the port 73 to the central bore,then through the restrictor 87 in the port 74 to a conduit 91, then intothe port 75 to the central bore, then through the restrictors 88 in theport 76 to a conduit 92 and then to the reservoir 12. The spool 77 isshown in an intermediate position in which the lands 79 and 81 occludesome of the restrictors 87 and 88, respectively, allowing flow onlythrough the remainder of them. These restrictors reduce the noise whichotherwise would be generated by the throttling action of the lands. Ithas been found helpful to pass the fluid through two sets of restrictors87 and 88 although this is not necessary for the purposes of the presentinvention.

Three solenoid operated valves, denoted generally by the referencecharacters 94, 95 and 96, are provided to enable the apparatus tooperate in either of two modes. The valve 94 includes two lands 97 and98 and an operating winding 99. In the de-energized position shown, aninlet conduit 101 communicates with an outlet conduit 102 while anotherinlet conduit 103 is occluded. When the winding 99 is energized, theconduit 101 is occluded while the conduit 103 communicates with theconduit 102. Similarly, the valve 95 includes lands 104 and 105 and anoperating winding 106. In the de-energized position shown, a conduit 107communicates with the conduit 101 while a conduit 108 is occluded. Whenthe winding 106 is energized, the conduit 107 is shut off while theconduit 108 communicates with the conduit 101. The valve 96 includeslands 111 and 112 and an operating winding 113. This valve is shown inits energized position in which a conduit 114 communicates with theconduit 107 while in the deenergized position the conduit 114 is cutoff. The remaining conduit 115 of the valve 94 is sealed off and is notused. The conduit 114 is connected to the junction of the restrictors inthe pressure divider 23, that is, to a point between the restrictor 24and the nozzle 61.

One terminal of each of the windings 99, 106 and 113 is grounded. Theother terminal of the winding 113 is connected to the lower contact 121of a single pole double throw switch 122. This switch serves to connectone side of the power line 123 to either the contact 121 (as shown) or acontact 124 which is connected to the conductor X. The conductor Xinterconnects the contact 124 with the terminal 43. The remainingterminals of the winding 99 and 106 are connected to conductors Z and Yrespectively, which, in turn are connected to the contacts 42 and 41,respectively. The intermediate portions of the conductors X, Y and Zhave been omited in order to simplify the drawing.

The apparatus of FIG. 2 operates in substantially the same manner,except for details, as has been explained in connection with FIG. 1. Itwill be assumed at first that the switch 122 is in the position shownwhere it energizes the winding 113 but not the conductor X with theresult that the valves 94, 95 and 96 are in the positions shown in thedrawing. The conduit 114 communicates through these valves with theconduit 86 and the end space 71. The position of the spool 77, and theflow rate through the valve 17 are responsive to the pressure in thisend space 71.

The pump 11 supplies fluid through the check valve 31 to the loads andto the accumulator 14. In the position shown in FIG. 2, the accumulatoris substantially full, that is, it contains substantially the maximumquantity of fluid it is capable of storing. In this position, the tailrod 32 is down and the arm 38 engages the contact 41 but this has noeffect at this time because the conductor X is not energized. The arm 44has operated the chain 45, the sprockets 47 and 48, the gears 49 and 51and the cam 53 to the positions shown at which the arm 55 is atsubstantially its most leftward position so that the member 62 is asclose as possible to the nozzle 61 and the restrictor 25 hassubstantially its maximum value. Thus the pressure drop across therestrictor 25 and the pressure in the conduit 114 and the end space 71are substantially maximum and the valve spool 77 is urged against thespring 83 to the position shown at which the valve 17 is capable ofdiverting the entire output of the pump 11 to the reservoir 12.

If now the load should increase so as to require a greater rate of fluidflow, it would tend to draw fluid from the accumulator 14. The cam 53would rotate clockwise, allowing the arm 55 and the member 68 to beurged to the right by the spring 66, thereby decreasing the magnitude ofthe force on member 62 which in turn decreases the pressure drop acrossrestrictor 25 and decreases the pressure in the end space 71. The spring83 would then urge the spool 77 to the right, decreasing the portion ofthe pump output which is diverted to the reservoir 12, making moreavailable to the load and the accumulator. An equilibrium position wouldsoon be reached with the valve 17 passing the excess of pump output oversystem demand.

With the switch 122 in the upper position, the winding 113 isdeenergized so that the valve 96 shuts off the conduit 114. Thus, thepressure divider 23 and its associated apparatus have no effect. Withthe contact 124 and the conductor X energized, the valves 94 and 95 arecontrolled by the position of the accumulator tail rod 32. In theposition shown, the accumulator is full, the arm 38 engages the contact41, conductor Y and winding 106 are energized, while conductor Z andwinding 99 are de-energized. The end space 71 communicates, throughconduits 86 and 102, valves 94 and 95, conduit 108 and filter 26 withthe load line 13 with the result that this high pressure overcomes thespring 03 and opens the valve 17 fully so that the entire output of thepump 11 is diverted to the reservoir 12 while the accumulator 14supplies the entire load. As fluid is first drawn from the accumulator14, the tail rod 32 rises, disengaging the arm 38 from the contact 41thereby deenergizing conductors Y and the winding 106. The valve 95reverts to the position shown in the drawing, closing the connectionbetween the load line 13 and the end space 71. However, the valve 17remains in its fully open position because the hydraulic lock created bythe closure of all connections to the end space 71 maintains thepressure in this space and holds the valve 17 open. When the accumulator14 is nearly empty, the moveable arm 38 engages the contact 42 therebyenergizing the chamber Z and the winding 99. The valve 94 connects theend space 71 to the reservoir 12 thereby closing the valve 17 so thatthe entire output of the pump 1 1 goes to the load and the accumulator14, none being directed to the reservoir 12. Hydraulic lock holds thevalve 17 closed when the arm 38 is disengaged from stances in which theo en-closed mode jlust described can be used to a vantage. However, 1 isusually preferred to operate the system in the continuously variablemode with the pressure in the end space 71 controlled continuously bythe amount of fluid stored in the accumulator 14. In this mode thecyclic changes of pressure in various parts of the apparatus resultingfrom discontinuous operation are avoided. Likewise, the movements of thepiston 15 in the accumulator are minimized.

. It will be understood that the drawing is schematic only and that anactual system may include additional apparatus such as safety valves,limit switches and the like. However, such items have been shown becausethey are well known and do not form a part of the present invention.

Although a preferred embodiment has been described in considerablydetail for illustrative purposes, many modifications can be made withinthe spirit of the invention. Therefore, it is desired that theprotection afforded by Letters Patent be limited only by the true scopeof the appended claims.

What is claimed is:

1. An hydraulic power supply system, comprising,

a reservoir containing a supply of fluid,

an accumulator for storing fluid under pressure,

a load line connected to said accumulator,

a continuously running pump including an inlet connected to saidreservoir and an outlet connected to said load line and to saidaccumulator,

a variable flow rate valve including an inlet connected to said outletof said pump and an outlet connected to said reservoir,

first and second restrictors serially connected between said load lineand said reservoir,

means for varying the magnitude of said second restrictor in accordancewith the variations in the quantity of fluid in said accumulator wherebythe pressure at the junction of said restrictors constitutes a controlpressure, and

means responsive to said control pressure for continuously controllingthe rate of flow of fluid through said valve.

2. An hydraulic power supply system in accordance with claim 1, in whichsaid second restrictor includes a nozzle through which fluid flows andalso includes a member formed with a flat surface positioned adjacent tosaid nozzle for intercepting the flow of fluid therethrough and in whichsaid means for varying in cludes means for controlling the position ofsaid member in accordance with the quantity of fluid in saidaccumulator.

1. An hydraulic power supply system, comprising, a reservoir containinga supply of fluid, an accumulator for storing fluid under pressure, aload line connected to said accumulator, a continuously running pumpincluding an inlet connected to said reservoir and an outlet connectedto said load line and to said accumulator, a variable flow rate valveincluding an inlet connected to said outlet of said pump and an outletconnected to said reservoir, first and second restrictors seriallyconnected between said load line and said reservoir, means for varyingthe magnitude of said second restrictor in accordance with thevariations in the quantity of fluid in said accumulator whereby thepressure at the junction of said restrictors constitutes a controlpressure, and means responsive to said control pressure for continuouslycontrolling the rate of flow of fluid through said valve.
 1. Anhydraulic power supply system, comprising, a reservoir containing asupply of fluid, an accumulator for storing fluid under pressure, a loadline connected to said accumulator, a continuously running pumpincluding an inlet connected to said reservoir and an outlet connectedto said load line and to said accumulator, a variable flow rate valveincluding an inlet connected to said outlet of said pump and an outletconnected to said reservoir, first and second restrictors seriallyconnected between said load line and said reservoir, means for varyingthe magnitude of said second restrictor in accordance with thevariations in the quantity of fluid in said accumulator whereby thepressure at the junction of said restrictors constitutes a controlpressure, and means responsive to said control pressure for continuouslycontrolling the rate of flow of fluid through said valve.